A. Field of the Invention
The present invention relates to log carrying trailers, and particularly to an improved chassis of a log carrying trailer.
B. Description of the Prior Art
Truck-trailer units are generally utilized in the hauling of cut timber from a cutting area to a mill site to be processed. The terrain over which trucks and trailers haul logs is extremely rough, characterized by unpaved, rarely graded gravel roads cut from forested areas for the express purpose of removing logs. As a result, the equipment used to haul logs, and especially the trailer chassis, which typically must support a load of up to 28,600 pounds, is subjected to tremendous stresses as they are driven down steep uneven mountain logging roads. Consequently, there is experienced in the log hauling business numerous equipment failures, including structural damage to the trailer chassis.
The typical prior art trailer chassis design comprises three basic elements: first, the log bunk which retains the logs on the chassis in a secure fashion; secondly, a bridge beam pivotally connected to the log bunk; and thirdly, the main chassis portion which is affixed to the multiple axles commonly used. The log bunk is affixed to the bridge beam by a "cup and saucer" apparatus which permits rotation of the bunk on top of the permanently affixed bridge beam. The bridge beam is necessary due to the system of measuring the weight of logs carried, which is commonly done by scale pads near the outermost lateral end of the bridge beam. The bridge beam is fixedly attached to the chassis, and at the lateral uppermost edges of the chassis, where it is in partial contact with the bridge beam, there are the compression scale pad devices used to weigh the log load.
The prior art chassis design is commonly a truncated "A" shape, with a flat horizontally-aligned upper surface, to which is affixed the bridge beam, and a pair of outwardly flared depending legs which are the primary support structures of the chassis. There is a walking beam axle member attached to the lower portion of each leg, which is supported typically on two pairs of wheels on each side of the chassis.
The chassis portion of the prior art trailer design has front and back sides, a flat top portion and lateral sides extending from the upper surface to the bottom of the legs. There is no enclosing lower portion connecting the front and back sides. The legs are typically made of one piece of heavy gauge rolled steel which is bent in a three-sided fashion to resemble a block "C", with the side facing the opposing leg open, as well as the bottom facing portion between the front and back sides. There is typically a structual bracing member welded between the legs on the inside of the front and back pieces.
In the conventional prior art logging truck trailer chassis, at the approximate center of the upper portion, there is a through hole extending through the chassis extending from front to back, the through hole being four-sided and either square or rectangular in shape. With tubular extensions from the front and back sides at the through hole, a reach tube is formed which accepts the reach, an extensible elongate member attaching the trailer chassis to the towing vehicle. The reach tube has the four sides aligned parallel and perpendicular to the flat top portion of the main chassis.
U.S. Pat. No. 3,370,866, Mitchell, et al, discloses one type of prior art log trailer chassis with an improved supporting member for the log bunk. The wear surfaces of the supporting members are replaceable within permanent turntable members, and the rub irons subject to wear are also replaceable.
U.S. Pat. No. 3,350,116, Skirvin, et al, shows a bunk which is easily rotatable about a vertical axis relative to the trailer for use in hauling very long logs. The rub irons are provided with bearings to allow the bunk to more easily rotate about the center vertical axis.
Because the durability of a log carrying trailer chassis is of primary importance due to the rough conditions under which it is utilized, there is a need for a trailer chassis which will withstand the stresses to which it is subjected with less down time for maintenance, and also have a longer life span. The chassis is continually subjected to stresses not only from the rough road bed but also from the shifting and bouncing of the logs carried thereon. Thus, the chassis must be constructed so that the stresses are distributed in a manner that no portion of the chassis is subjected to excessive loading.
Also, because the gross weight of the truck-trailer combination with a load of logs is regulated by statute, it is desirable to produce a carrying vehicle which weighs as little as possible, since every pound of weight reduction on the hauling vehicle results in an extra pound of logs which may be carried. For the independent or company logger, this means that more payload may be hauled per mile driven, thus decreasing the overall transportation costs.
In view of the foregoing, it is an object of the present invention to provide a log trailer chassis which weighs less than the conventional log trailer chassis currently in use, yet has improved stress-bearing characteristics resulting in less equipment failure and maintenance cost.